Nervous System Basics

Overview

• Importance of the nervous system: controls all physiological and psychological reactions.
• Central to all animal life except simple organisms like sponges.
• Nervous system functions: sensory input, integration, and motor output.

Nervous System Functions

• Sensory Input: Detection of stimuli (e.g., feeling a spider on your skin).
• Integration: Processing sensory input and deciding the response.
• Motor Output: Response execution (e.g., removing the spider).

Nervous System Organization

• Central Nervous System (CNS): Brain and spinal cord; main control center.
• Peripheral Nervous System (PNS): Nerves branching off from the brain and spinal cord, enabling CNS communication with the body.
  • Afferent (Sensory) Division: Sends sensory information to the CNS.
  • Efferent (Motor) Division: Sends instructions from CNS to muscles and glands.
    • Somatic Nervous System: Controls voluntary movements.
    • Autonomic Nervous System: Controls involuntary functions (e.g., heartbeat).
      • Sympathetic Division: Activates fight-or-flight response.
      • Parasympathetic Division: Calms the body down.

Nervous Tissue

• Composed mainly of cells, with neurons and neuroglia being the primary types.

Neurons

• Characteristics:
  • Long-lived, irreplaceable, high metabolic rate.
• Structure:
  • Soma (Cell Body): Contains nucleus and organelles.
  • Dendrites: Receive messages from other cells.
  • Axon: Transmits impulses away from the cell body.

Neuron Types

• Multipolar Neurons: Multiple processes; most common.
• Bipolar Neurons: Two processes; rare, found in sensory organs.
• Unipolar Neurons: Single process; mostly sensory receptors.

Neuron Functions

• Sensory (Afferent) Neurons: Transmit impulses toward CNS.
• Motor (Efferent) Neurons: Transmit impulses away from CNS.
• Interneurons: Transmit impulses within CNS.

Glial Cells

• Support and protect neurons; make up about half the brain's mass.

Central Nervous System Glial Cells

• Astrocytes: Anchor neurons to blood supply.
• Microglial Cells: Main immune defense in the CNS.
• Ependymal Cells: Produce and circulate cerebrospinal fluid.
• Oligodendrocytes: Create myelin sheath in CNS.

Peripheral Nervous System Glial Cells

• Satellite Cells: Support neuron cell bodies in PNS.
• Schwann Cells: Create myelin sheath in PNS.

Neural Communication

• Nerve cells use chemistry and electricity for communication.
• Details on communication processes will be covered in future content.